Oil and natural gas platforms and installations have a limited life of operations. When oil runs out, the platforms and installations are decommissioned using a number of different alternatives. As examples, the platforms and installations may be (a) left completely or partially in the water (often called “reefing”); (b) removed and then reused in another location; or (c) hauled to shore for scrapping or recycling.
The majority of platform decommissioning in the world has occurred in the Gulf of Mexico. The process of decommissioning typically begins with well abandonment in which the well bores are filled with cement. The vertical pipes that carry the oil and gas are then removed. In the past, use of explosives was the most commonly used method for removing the vertical pipes. However, the use of explosives has become controversial because explosions, particularly underwater explosions, generate intense shock waves that cause instantaneous lethal impacts for marine life residing on or near the platform structure. As a result, non-explosive methods have become the preferred method of removing vertical pipes.
One of the problems encountered while using non-explosive methods to remove vertical pipes during decommissioning is that the vertical pipes usually have been exposed to the marine elements for several years, if not decades. This exposure typically causes excess rust to form on steel components of the vertical pipes, particularly around the flanges and flange bolts that are used to connect sections of vertical pipe. The excess rust can significantly delay the removal of vertical pipes because of the added difficulty in removing flange bolts. These delays can add to the costs of decommissioning, which have been estimated to be in the range of $15 million to $20 million for removal of a complete platform in shallow waters such as the Gulf of Mexico. These costs are typically borne by the lease operator, who is consistently searching for ways to reduce costs of decommissioning.